17th July 2026
What Are Primers and How Do They Differ?
A good coating system is only as strong as the surface underneath it.
That is why primers play such an important role in protecting steel, aluminium and other materials. The right primer can improve adhesion, increase corrosion resistance and help the finished coating last considerably longer.
But not all primers do the same job.
Choosing between a zinc-rich primer, epoxy primer, high build primer or etch primer depends on the material being coated, where it will be used and the level of protection required. In this guide, we look at the main types of primer, how they work and where each is best used.
What Is a Primer?
A primer is the first coating applied to a prepared surface before the final topcoat or finishing system. Its job is to create a strong base for the coating system while helping to protect the material underneath.
Depending on the type of primer used, it can help to:
• Improve adhesion between the surface and the topcoat
• Protect steel against corrosion
• Provide additional resistance to moisture and chemicals
• Smooth minor surface imperfections
• Improve the overall lifespan of the coating system
For industrial metalwork, choosing the correct primer is particularly important. The primer must be compatible with both the material being coated and the final coating system. Proper surface preparation is equally important, which is why processes such as shot blasting often form the first stage of a professional industrial coating process.
A Brief History of Primers
The idea of preparing a surface before applying a decorative finish has been around for centuries. Early civilisations used natural materials to create base layers for pigments and paints. The development of modern synthetic coatings during the 20th century transformed the industry, introducing primers capable of providing far greater adhesion, corrosion resistance and durability.
Today, industrial primers are a fundamental part of many protective coating systems, particularly when steelwork or metal components will be exposed to moisture, chemicals or demanding environments.
What Are the Different Types of Primer?
Zinc-Rich Primers
Zinc-rich primers are commonly used on steel where a high level of corrosion protection is required. They contain a high proportion of zinc particles which help protect the underlying steel.
How Does a Zinc-Rich Primer Work?
Zinc provides what is known as sacrificial protection. If the coating becomes exposed to moisture or corrosive conditions, the zinc corrodes in preference to the steel underneath. This can significantly slow down the corrosion process and extend the life of the component. Zinc primers are often used for structural steel, external metalwork and equipment that may be exposed to demanding environments.
Advantages:
• Excellent corrosion protection
• Suitable for demanding industrial environments
• Can significantly extend the lifespan of steelwork
Disadvantages:
• Requires good surface preparation
• Usually more expensive than a basic primer system
• Must be correctly matched with the intended topcoat For the best performance, steel will normally need to be properly prepared before coating.
At NSP Coatings, this can include shot blasting to remove contamination and create the correct surface profile before the primer is applied. Where long-term corrosion protection is required, hot zinc spray may also be considered as an alternative or part of a wider protective coating specification. Leading manufacturers include Hempel, PPG Protective & Marine Coatings and Jotun.
Epoxy Primers
Epoxy primers are widely used within industrial coating systems because of their excellent adhesion, durability and resistance to moisture and chemicals. They are particularly effective on steel and can also be suitable for aluminium when used as part of the correct system.
How Does an Epoxy Primer Work?
Once cured, an epoxy primer creates a hard and durable barrier between the substrate and the surrounding environment. It also provides a strong base for subsequent topcoats.
Advantages:
• Excellent adhesion
• Good chemical resistance
• Strong resistance to moisture
• Suitable for demanding industrial applications
Disadvantages:
• Can require longer curing times than some other primers
• Careful surface preparation is essential
• The correct overcoating window must be followed
Epoxy primer systems are commonly used alongside [wet spray coatings – LINK TO WET SPRAY PAGE] where a specification requires a durable multi-coat protective finish. Leading manufacturers include Axalta, Sherwin-Williams and BASF.
High Build Primers
High build primers are designed to create a thicker coating layer than a standard primer. This additional film build can help provide a more uniform surface and reduce the appearance of minor imperfections before the topcoat is applied.
How Does a High Build Primer Work?
High build primers contain a higher level of solids, allowing a greater coating thickness to be achieved during application. Depending on the product, they may also help to fill minor marks and surface irregularities.
Advantages:
• Creates a more uniform surface
• Can help reduce the appearance of minor imperfections
• Provides additional coating thickness
• Creates a good base for finishing coats
Disadvantages:
• May require additional application and curing time
• Not a substitute for proper surface preparation
• Some systems can add to the overall coating cost High build primers are commonly used where the appearance of the finished product is particularly important or where a specified coating thickness needs to be achieved. Leading manufacturers include PPG and AkzoNobel.
Etch Primers for Aluminium
Aluminium and other non-ferrous metals can present different coating challenges to steel. Etch primers are specifically designed to promote adhesion to difficult surfaces such as aluminium.
How Does an Etch Primer Work?
An etch primer contains components that react with the metal surface, creating a better key for subsequent coatings. This helps the coating system adhere more effectively to the substrate.
Advantages:
• Improves adhesion to aluminium and other non-ferrous metals
• Provides a suitable base for subsequent coatings
• Can help provide additional protection against oxidation
Disadvantages:
• Designed primarily for specific substrates
• Correct application is important
• Not suitable for every coating specification
The preparation of aluminium is particularly important before coating. Depending on the specification, this may involve specialist aluminium preparation before the primer and final coating system are applied. Leading brands include DuPont, Rust-Oleum and 3M.
Acrylic Primers
Acrylic primers are versatile primers used across a wide range of applications and materials. Many are fast drying and can provide a practical base for different topcoat systems. However, acrylic primers generally do not offer the same level of heavy-duty protection as specialist epoxy or zinc-rich systems.
Advantages:
• Fast drying
• Versatile
• Compatible with a range of coating systems
Disadvantages:
• Generally less suitable for highly corrosive environments
• May provide less protection than specialist industrial primers
• Performance depends heavily on the complete coating system
Leading brands include Zinsser and a range of specialist industrial coating manufacturers.
Why Is Primer So Important?
Applying primer is not simply another stage in the painting process. On the right project, it can be fundamental to the performance of the entire coating system.
Better Adhesion
The primer creates a strong connection between the prepared substrate and the finishing coat, reducing the risk of peeling or premature coating failure.
Corrosion Protection
Zinc-rich and epoxy primers can provide an important additional layer of protection against rust and corrosion.
A Better Finished Surface
High build primers can help create a more consistent base before the final coating is applied.
Resistance to Harsh Environments
Certain primer systems provide additional resistance against moisture, chemicals and industrial conditions.
Longer Coating Life
By combining the correct surface preparation, primer and topcoat, the complete coating system can provide significantly better long-term performance.
Do You Always Need a Primer?
Not necessarily. Whether a primer is required depends on the material, the environment and the coating system being specified. Some powder coating systems may be applied directly to correctly prepared metal, while other applications benefit from an additional primer layer to improve corrosion resistance.
Industrial wet spray coating systems may use one or several primer, intermediate and finishing coats depending on the specification. The important thing is to look at the complete system rather than simply choosing a primer in isolation.
Choosing the Right Primer for Your Project
There is no single primer that is right for every job. Before choosing a coating system, you need to consider:
• The type of metal being coated
• Whether the product will be used indoors or outdoors
• The level of exposure to moisture or chemicals
• The required lifespan of the coating
• The required finish
• The intended topcoat
• Any industry or project specifications
At NSP Coatings, we look at the complete job, from surface preparation and shot blasting through to the primer and final powder coating or wet spray finish. This helps ensure that every stage of the process works together.
The Right Primer Is Part of the Right Coating System
Primers can make a major difference to the adhesion, durability and corrosion resistance of a finished coating, but they cannot compensate for poor preparation or an incorrectly specified coating system. The best results come from combining the correct surface preparation, primer and topcoat for the environment in which the finished product will be used. At NSP Coatings, our team can help you identify the most suitable coating system for your project, whether that involves shot blasting, powder coating, wet spraying, hot zinc spray or a combination of protective coatings.
Contact NSP Coatings to discuss your project and we will help you work out the best approach.
